Why do some "ring main unit gas boxes" have observation windows while others do not? What is their f

1. The observation window on the gas box of the ring main unit is a common design, mainly used to facilitate operators to observe the opening and closing positions and fracture status of the isolation switch/grounding switch inside the cabinet. Why do some ring main unit gas boxes have observation windows, while others do not? Is it necessary to configure them?

2. Whether the ring main unit should be equipped with observation windows and air box types is closely related: - SF ₆ Fully sealed air box: often without observation windows, relying on pressure gauges/density relays for monitoring, with a more compact structure and more reliable sealing. -Environmentally friendly gas (dry air/nitrogen) box: equipped with observation window, used to check the position of isolation switch/grounding switch, which is generally required by State Grid standards. -Solid insulated/air insulated ring main unit: There must be an observation window for viewing the position of the isolation knife/circuit breaker.

3. Why are environmental protection and solid gas tanks necessary, but SF6 is not? The differences in the necessity of observation windows are determined by the characteristics of the insulation medium and the methods of operation and maintenance confirmation

1) Environmentally friendly gases (dry air/nitrogen)/solid insulation: The reasons why they must be used are as follows:

-The arc extinguishing/insulation capability is weaker than SF ₆, and the opening and closing positions and contact states of internal contacts and isolation fractures are more critical for safe operation.

-This type of gas box structure is more open, and direct observation with the naked eye is the most intuitive and reliable way to confirm the position during operation and acceptance, which is also a mandatory requirement of mainstream network standards.

-Five proof logic verification and troubleshooting need to be completed through observation windows, as the absence of windows will significantly increase operational risks.

2) SF ₆ Ring main unit: The reasons for not matching are as follows:

-SF has extremely strong insulation and arc extinguishing performance, and the gas box is mostly a fully sealed welded structure with extremely high sealing requirements.

-Opening the observation window will add an additional sealing surface, increasing the risk of air leakage, and the core requirement of SF air boxes is long-term maintenance free and minimal leakage points.

-The status can be remotely/locally confirmed through position indicators, electrical auxiliary contacts, and live display devices, without the need to open windows for visual inspection, which can meet the needs of operation and maintenance.

4. Summary:

Environmental protection/solid insulation relies on visually confirming the internal state, so an observation window must be provided; SF ₆ prioritizes ensuring that the seal does not leak, and electrical/mechanical indicators can be used instead of observation, so it is not necessary.